Magnetic monopole polarons in spin ice with mixed coordination numbers

Emergent quasiparticles that arise from the fractionalization of the microscopic degrees of freedom have been one of the central themes in modern condensed matter physics. The notion of magnetic monopoles, freely moving quasiparticles fragmented from local dipole excitations, has enjoyed much success in understanding the thermodynamic, static, and transport properties of the so-called spin-ice materials. The artificial version of spin ice, where a lattice of nanoscale magnetic dipoles is sculpted out of a ferromagnetic film, provides a unique opportunity to study these unusual quasiparticles in a material-by-design approach. Here we show that the elementary excitations in the ice phase of a nano-magnetic array arranged in the pentagonal lattice are composite objects comprised of the emergent monopole and a surrounding cloud of opposite uncompensated magnetic charges.